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Thursday, July 31, 2008

Exploring Focal Lengths

Changing your focal length can do much more than simply give you a wider or more telephoto shot



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Your choice of focal length affects more than merely the amount of the scene you can capture from a given distance. It also affects the way that objects appear in relation to one another, depth of field and more. Compare the top image on the opposite page, which was shot with a 200mm lens, with the image above, which was shot at 50mm. The bottom image on the opposite page may look telephoto at first glance, but it was shot at 14mm from a very close distance.

Perspective And Focal Length
By changing focal length and your distance to a subject (you must do both), you can change how perspective looks in a photograph. Perspective in a photograph relates to how objects in a scene change in size as they move closer or farther from the camera; it comes from a relationship of size and distance.

Imagine that you hold two same-sized basketballs in your hands. If you bring one close to your eyes and keep the other at arm's length, the one closer to you looks bigger. If you hold them at the same distance, they're the same size. A painter creates the appearance of depth in a painting by changing this relationship—when the artist puts these balls onto a plain background, he or she can make the balls look the same size or radically different in size, changing how you see the distance between them. This relationship of size and how we perceive distance is what perspective is all about.

These compositions appear nearly identical until you look more closely at the background. The image on this page was shot at 23mm, while the image on the opposite page was shot at 14mm. Though the tree in the foreground is essentially the same size in both images, much more of the background is captured in the 14mm shot.

You quickly can see how using a zoom lens can alter perspective. A digital camera is great for this because you can see the effects immediately when you review the photos in the LCD.

Go to the widest zoom setting of your lens. Get close enough to your subject so that it fills most of the distance from the top to the bottom of your photo and take a picture. Next, zoom in to the most telephoto setting of your lens. Then back up until your subject once again fills most of the distance from the top to the bottom of your photo—you're trying to keep your subject approximately the same size. Take the picture.

When you compare the two photos, you immediately see a change in the background. Even though you know the distance between the subject and the background didn't change, it looks like it did! The wide-angle shot has a background that looks much farther away from the subject than the telephoto shot. The wide-angle image, therefore, has a deeper perspective, while the telephoto image has a flatter perspective.

Give your photograph a sense of the subject's environment by using a wide-angle lens. That lens shows off your subject and gives a little space around it, allowing your viewer to see its location.

On the other hand, use a telephoto to compress the distance from foreground to background and make the subject look like it's packed in with a lot of other things. With really strong telephoto lenses, this can make objects look like they're right on top of each other when, in fact, they're not in real life. This is a Hollywood trick used in movies to make it look like the hero is about to be run over by a truck, for example, when the truck really isn't that close.

You can use perspective control for creative effect or you can use it to make a livelier and more interesting photo. A sun setting over the mountains may look fine with a mid-range focal length, but change to a strong telephoto and the mountain ridges become more dramatic against a larger sun. Or with a really wide-angle lens, you can get up close to a subject and make it totally dominate the rest of the image.




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